Johannsenite

johannsenite

rhodonite

xonotlite

hedenbergite

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Formula: CaMnSi2O6
Inosilicate (chain silicate), clinopyroxene, forms a series with hedenbergite and with diopside, manganese-bearing mineral
Specific gravity: 3.56
Hardness: 6
Streak: White
Colour: Blue-green, grey-white, dark brown, colourless
Common impurities: Ti,Al,Fe,Mg,Na,K,C,P,H2O

Environments:

Metamorphic environments
Hydrothermal environments

Johannsenite is found in contact metamorphic environments, in skarn, and less commonly in quartz or calcite veins cutting rhyolite. It is characteristic of metasomatised limestone adjacent to acid and intermediate intrusions, where it is often associated with rhodonite and bustamite. Associated minerals include rhodonite and manganese oxides (HOM, Dana).

Localities

There are three co-type Localities, the Temperino Mine, Campiglia Marittima, Livorno Province, Tuscany, Italy, Civillina Mountain, Recoaro Terme, Vicenza Province, Veneto, Italy, and the Franklin Mine, Franklin, Franklin Mining District, Sussex County, New Jersey, USA.

At the Woods Mine, Darling county, New South Wales, Australia, johannsenite has been found as radial aggregates intergrown with serandite, quartz and minor manganiferous aegirine. It appears that the upper temperature limit during the metamorphosis of the Woods mine manganese deposit was about 300C to 500C (AJM 15.1&2.15-17).

At the North Mine, Broken Hill, Broken Hill district, Yancowinna county, New South Wales, Australia, johannsenite occurs as ferroan material with pyrosmalite-(Mn) and bustamite (Dana).

At Tetela de Ocampo, Tetela de Ocampo Municipality, Puebla, Mexico, johannsenite occurs in calcite veins in rhyolite and is altered to rhodonite and xonotlite and calcite (DHZ 2A p421, Dana).

At the Franklin Mine, Franklin, Franklin Mining District, Sussex County, New Jersey, USA, johannsenite occurs with rhodonite in interstices of andradite-manganophyllite breccia (Dana).

At the Triple Trip Mine (Brown Mule Mine), Copper Creek, Mason county, Washington, USA, johannsenite occurs as veins in rhodonite (Dana).

Alteration

johannsenite and H2O to rhodonite and xonotlite
6CaMnSi2O6 + H2O → 6Mn2+SiO3 + Ca6Si6O17(OH)2
(DHZ 2A p421).

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